1. Field of the Invention
The present invention relates to a semiconductor device having an improved semiconductor package structure, and particularly to a semiconductor device incorporating therein optical elements such as a photosensitive element or a light emitting element.
2. Description of the Related Art
In recent years, an optical transceiver suitable for use in a data communication system typified such as by Local Area Network (LAN) needs to operate at higher speed and be fabricated at lower cost and in smaller size. Typically, the optical transceiver has provided therein a Laser Diode (LD) and a Photo Diode (PD) in addition to an electrical circuit such as a Large Scale Integrated Circuit (hereinafter, referred to as LSI). Furthermore, in terms of optimal design for optical system, optimal packaging and optimal sealing, an optical element needs to be handled in a manner different from that employed to handle an LSI, etc., causing the cost of an entire package to increase.
In order to lower the cost of a package, approach to packaging optical elements has been made and a packaging substrate referred to as a CAN package or a Si bench has been proposed. The CAN package is constructed such that only optical elements are mounted on a Si substrate (hereinafter, referred to also as optical element mounting substrate), etc., on a transmission-side or components ranging from optical elements to a front-end IC (amplifier) are mounted on a Si substrate, etc., on a reception-side and those elements or components are hermetic sealed, and further, a signal is retrieved via a lead line (Hans L. Althaus et. al. IEEE TRANSACTIONS ON COMPONENTS, AND MANUFACTURING TECHNOLOGY vol. 21, pp. 147-156, May 1998). That is, LD, PD, etc., mounted on a Si substrate or the like are sealed within a housing and an input/output signal to and from LD or PD is transmitted via a lead line extended outside the housing. A Si bench generally has high thermal conductivity and is an assembly substrate comprising a Si substrate advantageous for incorporating thereon optical elements and selected in terms of flatness and workability, optical elements mounted on the Si substrate, and a resin encapsulating the Si substrate together with the optical elements (K. Kurata et al. Proc. Conf. 45th ECTC pp. 759-765 1995).
However, the CAN package has the following drawbacks. That is, in the CAN package, a signal is transmitted via a lead line and when a high-frequency signal is transmitted, large parasitic inductance and large parasitic capacitance generated within the CAN package prevent the signal from being transmitted at high speed. Furthermore, it is preferable to dispose a driver LSI (Large Scale IC) in the vicinity of an optical element that outputs and/or receives a weak signal. However, in the case of CAN package, since the optical element such as a PD or an LD is sealed within a housing, reduction of a distance between the optical element and the driver LSI becomes limited. Moreover, since the optical element is sealed within the housing, thermal conductivity of the CAN package unfavorably is lowered.
Furthermore, in the case of Si bench, since optical elements are mounted on a Si substrate, an LSI formed on the Si substrate can also be mounted in the vicinity of the optical elements and further, since the Si substrate has high thermal conductivity, the Si substrate has a high heat removal ability. However, an insulation film formed on the Si substrate is thin since the film is formed by thermally oxidizing the Si substrate and therefore, a problem occurs when a signal is transmitted within the Si bench, in other words, a signal is not transmitted at high speed within the Si bench.
As described above, the conventional technique does not yet provide a semiconductor device that is free from the above-stated problems, i. e., enables a signal to be transmitted at high speed within the device and further allows the optical elements to easily be mounted therein. In more detail, when modulating a signal at high frequency on the order of not less than about 1 GHz, parasitic capacitance due to the assembling probably makes device performance significantly degraded and accordingly, both a package design and an LSI design cannot be made without an analogue design technique for designing an optimal circuit taking into account how to incorporate leads of package, which leads have been assembled within the device in a compact manner, in addition to how to incorporate a mother board within the device and how to eliminate parasitic capacitance generated within the device.
For example, in the case of CAN package, etc., the parasitic inductance of a lead line and the parasitic capacitance of a bonding wire used to make connection of the optical element to the lead line largely affect device performance. Therefore, for example, when a transmission side is designed such that a driver LSI for driving an optical element is mounted on a mother board and a CAN package is connected to the mother board, an entire package should be designed taking into account the influence of the above-described parasitic inductance and parasitic capacitance.
Moreover, when the Si substrate, etc., is employed as a substrate that is used to mount an optical element thereon, the optical element is typically connected by wire bonding to the mother board on which a variety of LSIs for performing various processing are mounted. In this case, the inductance component of the wire acts as a reflection point that significantly echoes an electrical signal when the signal is modulated at high frequency and in addition, the wire needs to be encapsulated with a resin, thereby increasing the assembling cost. Additionally, since the Si substrate generally has interconnect lines formed on a silicon dioxide (SiO2) film as an insulation film, which is formed on the surface of the substrate by thermally oxidizing the substrate, the parasitic capacitance of the device consisting of the substrate is large and the device is not suitable for high frequency drive. For this reason, the SiO2 film has been formed to have a large film thickness. However, forming the SiO2 film to a large thickness unfavorably lowers the productivity of semiconductor device and its availability.
This increases the need for a highly advanced substrate capable of transmitting a signal at high frequency within the substrate and assembling optical elements in a compact manner. Furthermore, the development of a semiconductor package structure is indispensable for reduction of the cost of an optical transceiver, which structure can be constructed such that microelectronic components are physically assembled in the same manner as that employed in the conventional technique and electrically assembled in a complete fashion as well without taking into account how to incorporate therein optical elements when designing an entire package.
An object of the present invention is to provide a semiconductor package structure and having a high heat removal ability without sacrificing its electrical performance at high frequency and further, enabling time efficiency in package design associated with packaging or mounting and reduced packaging cost.
A semiconductor device according to the present invention comprises: an insulating film; first and second conductive layers formed on both surfaces of the insulating film and constituting wiring patterns respectively, the first and second conductive layers being constructed such that a part of each of the wiring patterns formed in the first and second conductive layers is a conductive wiring for a high-speed signal, designed taking into account high frequency characteristic of the conductive wiring based on characteristic impedance of the conductive wiring; an integrated circuit mounted on the first conductive layer; and a conductor connecting the wiring pattern formed in the first conductive layer and the wiring pattern formed in the second conductive layer to one another, in which the insulating film is further constructed such that a portion of the insulating film is mounted on a substrate used to mount thereon an object, the portion being occupied by the integrated circuit, and a connection portion for making connection to a different substrate is provided at an end of the insulating film located outside the substrate used to mount thereon an object.
The semiconductor device is constructed so that the insulating film is, for example, an insulating flexible film capable of changing a profile of the insulating flexible film and the substrate used to mount thereon an object is, for example, a silicon substrate or a metal substrate.
Preferably, the semiconductor device further comprises: a stiffener made of metal or alloy, and mounted on a circumference of the integrated circuit on the insulating film; a heat spreader supported by the stiffener and contacting the integrated circuit. Additionally, the device further comprises a heat sink provided to contact the heat spreader and having a plurality of fins provided therein.
A first semiconductor device incorporating optical elements therein comprises: an optical element mounted on the substrate used to mount thereon an object; a third conductive layer provided on the substrate used to mount thereon an object and constituting a wiring pattern; and a connection portion making electrical connection between the wiring pattern formed in the third conductive layer and the wiring pattern formed in the second conductive layer, and made from a solder or a gold bump.
The first semiconductor device incorporating therein optical elements is, for example, constructed such that an optical axis of the optical element is parallel to a surface of the substrate used to mount thereon an object and the device further includes: a side plate disposed on a side surface of the substrate used to mount thereon an object; a transparent window provided at a position of the side plate, the position being determined such that the side plate and the optical axis cross one another; and a transparent resin filling a space between the optical element and the transparent window. Moreover, the device, for example, further includes another integrated circuit mounted on the third conductive layer on the substrate used to mount thereon an object. Additionally, the device is, for example, constructed such that an optical axis of the optical element extends toward a surface of the substrate used to mount thereon an object in a direction vertical to the surface of the substrate used to mount thereon an object and the device further includes: a light reflecting portion formed of an inclined surface and provided at a position of a surface of the substrate used to mount thereon an object, the position being determined such that the surface and the optical axis cross one another; a side plate disposed on a side surface of the substrate used to mount thereon an object; a transparent window provided at a position of the side plate, the position being determined such that the side plate and the optical axis cross one another; and a transparent resin filling a space between the optical element and the transparent window. Moreover, the device is, for example, constructed such that the substrate used to mount thereon an object is a silicon substrate and the inclined surface is formed by etching with KOH, and a metal film is formed on the inclined surface by metallization to constitute the light reflecting portion. Alternatively, the device is constructed such that the substrate used to mount thereon an object is a metal substrate and the inclined surface is formed by mechanical processing to constitute the light reflecting portion.
A second semiconductor device incorporating optical elements therein in accordance with the present invention includes: an optical element mounted on the first conductive layer on the insulating film; a third conductive layer provided on the substrate used to mount thereon an object and constituting a wiring pattern; and a connection portion making electrical connection between the wiring pattern formed in the third conductive layer and the wiring pattern formed in the second conductive layer, and made from a solder or a gold bump.
The second semiconductor device incorporating optical elements therein is, for example, constructed such that an optical axis of the optical element extends toward a surface of the insulating film in a direction vertical to the surface of the insulating film and the device further includes: a hole or a transparent portion provided at a position of the insulating film, the position being determined such that the insulating film and the optical axis cross one another; a light reflecting portion for changing an orientation of the optical axis; a side plate disposed on a side surface of the substrate used to mount thereon an object; and a transparent window provided at a position of the side plate, the position being determined such that the side plate and the optical axis cross one another. Additionally, the device is, for example, constructed such that the light reflecting portion includes: an inclined surface formed on a surface of the substrate used to mount thereon an object; and a metal film formed on the inclined surface by metallizing the inclined surface. Moreover, the device is, for example, constructed such that an optical axis of the optical element extends remotely from a surface of the insulating film in a direction vertical to the surface of the insulating film and the device further includes: a light reflecting portion for changing an orientation of the optical axis in order to make the optical axis parallel to a surface of the substrate used to mount thereon an object; a side plate disposed on a side surface of the substrate used to mount thereon an object; and a transparent window provided at a position of the side plate, the position being determined such that the side plate and the optical axis cross one another. Still furthermore, the device is, for example, constructed such that the light reflecting portion is constituted by an inclined surface made from a metal member or an alloy member, and provided on a side opposite the optical element relative to the insulating film. Additionally, the device, for example, includes a lens disposed on the optical axis between the light reflecting portion and the inclined surface. In this case, the lens is a semi-spherical material provided in the inclined surface of the light reflecting portion and having a refractive index different from a refractive index of a portion surrounding the material. Moreover, a region between the optical element and the lens is preferably filled with a transparent resin.
Furthermore, in the present invention, for example, the substrate used to mount thereon an object includes: a fourth conductive layer formed on a rear surface of the substrate used to mount thereon an object; and a conductive layer for making electrical connection between the wiring pattern constituted by the third conductive layer and a wiring pattern constituted by the fourth conductive layer. In this case, the device according to the present invention preferably includes a fifth conductive layer formed on a surface of the another substrate, in which the substrate used to mount thereon an object is mounted on the another substrate and the wiring pattern constituted by the fourth conductive layer and a wiring pattern constituted by the fifth conductive layer are connected to one another. Moreover, the fourth conductive layer and the fifth conductive layer are preferably connected to one another through a solder or a gold bump.
Additionally, in the present invention, for example, the optical element constitutes two optical elements provided on the substrate used to mount thereon an object and the two optical elements consist are a photo sensitive element and a light emitting element respectively, and the semiconductor device further includes: an optical fiber disposed in a V-shaped groove provided in a surface portion of the substrate used to mount thereon an object; and a light guide for making optical connection between the photo sensitive element and the optical fiber and between the light emitting element and the optical fiber.
Moreover, in the present invention, for example, the integrated circuit includes: a pair of a first transmission integrated circuit and a first reception integrated circuit, mounted on one end of the first conductive layer; and a pair of a second transmission integrated circuit and a second reception integrated circuit, mounted on the other end of the first conductive layer and disposed at a location symmetric with respect to a point corresponding to the pair of the first transmission integrated circuit and the first reception integrated circuit, in which an input of the first transmission integrated circuit and an output of the second reception integrated circuit are connected to one another, and an output of the first reception integrated circuit and an input of the second transmission integrated circuit are connected to one another, and corresponding connection between the output and the input is made through the conductive wiring, formed in at least one of the first and second conductive layers, for a high-speed signal.
In the present invention, the first and second conductive layers are formed on front and rear surfaces of the insulating film and a part of each of the wiring patterns formed as the first and second conductive layers is made to be a conductive wiring provided for high-speed signal and designed taking into account its high frequency characteristic based on its characteristic impedance, and then, the LSI needed to provide advantage of transmitting a signal at high frequency is mounted on the insulating film, and further, a pad, formed on the integrated circuit, for high-speed signal is connected to the connection portion by making use of the conductive wiring for high-speed signal. Since the insulating film is formed in a manner different from that employed to form an insulating film on a Si substrate by means of thermal oxidation and can be formed to have a sufficient thickness, the wiring patterns constituted by the first and second conductive layers that are formed on front and rear surfaces of the insulating film are extremely advantageous for transmitting a signal at high speed and further can easily be designed to provide an advantage of transmitting a signal at high speed. Additionally, the optical element is mounted on a substrate for incorporating thereon an object, such as a Si substrate or a metal substrate having an advantage of incorporating thereon an element. Then, the insulating film is mounted on the substrate for incorporating thereon an object and electrical and mechanical connections are made therebetween, thereby achieving a semiconductor device that provides an advantage of transmitting a signal at high speed and incorporating therein an optical element in a compact manner. In addition, when the insulating film is an insulating flexible film capable of changing its profile, connection of the conductive wiring for high-speed signal to a different substrate can be made facilitated.
In a detailed aspect of the present invention, conductive layers are formed on both surfaces of the flexible film and wiring patterns are formed in the conductive layers on both surfaces of the flexible film made of an insulator capable of changing its profile to some extent, and if necessary, the wiring patterns on both surfaces of the flexible film are connected to one another through a conductor embedded in a hole 9 such as a via hole or a through hole. In this case, forming the wiring pattern in the conductive layer on at least one surface of the flexible film and on a part of the flexible film forms a transmission line (hereinafter, referred to as a conductive wiring for high-speed signal) whose characteristic impedance is previously and desirably calculated. Subsequently, an integrated circuit (hereinafter, referred to as LSI) is flip-chip mounted on the upper conductive layer and a microelectronic component such as a capacitor is mounted on the upper conductive layer, and a mass block (hereinafter, referred to as stiffener) having approximately the same height as those microelectronic components, i. e., the LSI and the capacitor, is mounted on a part of the flexible film so as not to adversely affect the characteristic impedance of the conductive wiring for high-speed signal. Furthermore, a heat spreader made of a metal plate having high electrical conductivity and high thermal conductivity is mounted on the flexible film and connected to the stiffener and the LSI so as to cover the LSI. Thus, an inexpensive package structure having an advantageous heat removal mechanism and improved efficiency in package assembly can be obtained.